A relay is a network node for enhancing the signal quality of the link between a base station and user equipment. The coverage and cell edge data rate can be considerably enhanced by using relays. There are three main categories of relays: layer 1, layer 2 and layer 3 relays. Layer 1 relays, also referred to as advanced repeaters, are expected to be one of the potential technology components for LTE (Long Term Evolution) Advanced which is an enhancement of 3GPP (3rd Generation Partnership Project) LTE. The terms ‘relay’ and ‘repeater’ are used interchangeably herein and mean the same thing unless otherwise noted. The main difference between an advanced repeater and a more conventional repeater is that an advanced repeater includes one or several advanced functions, such as frequency-selective amplification and controllability.
Frequency selective repeaters are particularly beneficial in OFDMA (Orthogonal Frequency-Division Multiple Access) systems where typically only part of the cell bandwidth (e.g., a sub-set of resource blocks) is used by one UE (User Equipment) at a time. A frequency selective repeater only amplifies the part of the allocated bandwidth for which there exists an association between UE and the repeater. A layer 2 relay also performs advanced functions such as decoding and correction of data before forwarding the data to the next hop towards UE or an eNodeB (enhanced node B). To enable these advanced functions, typical layer 2 related features such as scheduling, HARQ (Hybrid Automatic Repeat Request), MAC (Media Access Control) etc. are implemented in layer 2 relays. A layer 3 relay performs complete layer 3 related operations such as resource allocation, admission control etc. on the hop between itself and UE or between itself and the eNodeB. This requires the layer 3 relay to implement complete layer 3 protocol aspects in addition to lower layers (e.g., layer 1 and layer 2).
To make a repeater controllable by an eNodeB, a new interface between the eNodeB and the repeater referred to as the X3 interface has been recently introduced. Signaling alternatives for the X3 interface include PDCCH (Physical Downlink Control Channel)/PUCCH (Physical Uplink Control Channel) signaling or L1 signaling, MAC control PDU (Protocol Data Unit) signaling and RRC (Radio Resource Control) signaling. The same signaling alternatives may also apply to other types of relays, e.g. layer 2 and layer 3 relays.
As described above, the main objective of the relay is to improve the link quality so that coverage and cell edge bit rate can be increased without requiring additional base stations. Depending upon the type of relay, the relay is typically controlled, monitored and configured by the base station (e.g., eNodeB in LTE) or other network nodes such as a radio network controller or core network node. Depending upon various factors such as deployment scenario, system load, capacity/throughput targets etc., certain parameters in the relays need to be updated at least on a semi-static basis. Therefore a mechanism is needed that allows the network (e.g. the base station) the possibility to configure and modify the parameters such as threshold levels for the algorithms used at the relay node, even for a frequency selective repeater.
Furthermore, a relay may also encounter problems and experience partial or complete disruption. This has a direct impact on network performance and therefore should be reported to the network. In response, depending upon the severity and the nature of the fault, the network node (e.g. base station) ideally trouble shoots or otherwise rectifies the problem via signaling to the relay. In general the communication between the relay and network node for the purpose of status reporting and configuration is mostly sporadic. In some cases the communication between the relay and network node is not time critical, e.g. when configuring thresholds for a particular algorithm used for amplifying a signal. It is also important that this type of signaling and message exchange between the relay and network node does not adversely impact or disrupt the normal relay operation. For instance, there should be minimal impact on the resources used for normal data or signaling transmission between UE and the base station via the repeater.
Existing UE protocol stacks (L1, MAC or RRC) are conventionally reused for the reporting of faults, etc. by relays. As such, relays are treated as if they were UE for all types of reporting to the network. Reusing the existing UE protocol stacks in this way leads to relatively simpler implementation and may not affect normal traffic between UE and network if done very rarely, e.g. during initial setup of the relay. However, relay configuration (e.g. reconfiguration of the UE-relay association) or reporting by the relay (e.g. error/faults, etc.) is part of the normal relay operation. Furthermore, the traffic/signaling between the eNodeB and relays may differ tremendously compared to that between eNodeB and UE. As such, reusing UE stacks for relays is not efficient enough. For example, if there are many relays frequently communicating with an eNodeB, there will be considerable signaling overhead, e.g. grants and assignments on PDCCH. The PDCCH capacity is quite limited to begin with and therefore at least its frequent use for communicating with relays should be minimized as much as possible. In general the radio resources should be used in a manner so that the impact on normal operation (i.e. between UE and network) is minimal.
As stated above, the signaling exchange between the network and relay for the purpose of configuration, error reporting, etc. is inevitable during relay operation. Such relay-to-network communication is referred to herein as reporting from the relay to the network or simply ‘relay reporting’. For the purpose of relay reporting, the use of normal radio resources and channels (e.g. PUSCH, PDCCH, etc.) is unavoidable, but should be minimal to reduce the impact on normal operation between UE and the network.